This invention relates to wastewater pollution monitoring and, more particularly, to a device and method for manually collecting for analysis relatively representative samples of wastewater containing materials not homogeneous within the effluent, such as, fats, oils and grease (FOG).
Wastewater samples taken for analysis and pollution control are obtained by two broad categories of sampling methods. One method takes a number of partial samples over a period of time and combines them into a composite sample in the same container. Composite sampling is carried out automatically, with the sample probe submerged in the effluent stream. Under normal circumstances, the composite sample method produces water samples which are most nearly representative of the wastewater flow and thus result in more precise and accurate analysis of the concentration of pollutants.
The second sampling method entails the taking of sequential or discrete samples which are generally referred to as grab samples. In its most basic form, a grab sample is obtained by placing a container, such as a bottle, into the flow of a wastewater stream and taking the collected sample to the laboratory for analysis. A grab sample, in effect, takes a single shot or stop action picture of the effluent flow and thus is less likely to produce an approximately representative sample. Nevertheless, government regulations dictate that analysis of FOG-containing wastewater be made from grab samples for seemingly logical reasons.
Fats, oils and greases (as well as numerous volatile organic compounds) invariably tend to float on the surface of water because of their relatively lower density. The submerged probe used in automatic composite sampling is ineffective to account for such layered flow. Recommended current practice suggests that grab samples be collected by filling the sample container just below the water surface of the flow channel and also that the sample be taken near the center of the flow channel where the turbulence is at a maximum. The obvious objective of such practice is an attempt to obtain a well mixed sample which is as homogeneous and representative as possible under the circumstances. Unfortunately, grab samples obtained as described are generally heterogeneous and seldom approximate a representative sample.
While efforts have been made to provide improved liquid sampling apparatus, I am not aware that they have successfully overcome the problem of sampling FOG-containing wastewater. For example, U.S. Pat. No. 4,317,378 shows a relatively complex device including counterweights and electrical actuators and timers designed to obtain a representative flow sample and filter out solids. Although the patented device conceivably might be used for composite or grab sampling, it does not address the question of obtaining a relatively homogeneous sample containing FOG.
There thus exists a need for a sample collecting device which automatically mixes the wastewater flow so that samples obtained thereby more nearly approximate a representative sample. There is also a need for a device of the character described which is portable and simple to use so that it may be applied as often and wherever required.